A box filled with 11 king melons has a mass of 12.04 kg. The same box when filled with 6 mangosteens has a mass of 1.24 kg. The mass of 1 king melon is six times the mass of 1 mangosteen. Find the mass of the box when it is empty. Express the answer in g.
1 kg = 1000 g

12.04 kg = 12040 g
1.24 kg = 1240 g

1 mangosteen = 1 u
6 mangosteens = 6 x 1 u = 6 u

1 box + 6 mangosteens = 1240
1 box + 6 u = 1240 --- (1)

1 king melon = 6 u
11 king melons = 11 x 6 u = 66 u

1 box + 11 king melons = 12040
1 box + 66 u = 12040 --- (2)

(2) - (1)
66 u - 6 u = 12040 - 1240
60 u = 10800

1 u = 10800 ÷ 60 = 180

6 u = 6 x 180 = 1080

From (1):
1 box + 6 u = 1240
1 box + 1080 = 1240
 
1 box = 1240 - 1080 = 160

Mass of 1 box = 160 g

Answer(s): 160 g